There has been a long felt need for the capability to measure the base altitudes of one to three kilometers thick clouds as viewed from above. Conventional space-based lidar methods measure cloud depths by direct transmission of a laser beam through the cloud and sensing the backscattered returns. These techniques are limited by severe optical scattering by cloud particles to thickness less than 500 meters. Meteorological satellite images and Shuttle lidar data reveal transparent spaces even under dense cloud conditions. Representative albedos are diffuse reflectivities for cloud and surface features and are well known data from satellite meteorological measurements. Clouds are classified in various forms. Cumulonimbus clouds are thick and large with a 92% albedo. Stratus clouds are thick and usually over an ocean with a 64% albedo. Cirrus clouds are isolated clouds over land with a 36% albedo. Land features are also classified in various forms. Light sand including white sands has a 60% alebdo. Dark sands including sands in valleys, plains and slopes have a 27% albedo. Snow has a 59% albedo. Arctic summer ice has a 50% albedo. Coniferous forests have a 12% albedo. Oceans have a 7% albedo.
Current methods involve the propagation of a lidar beam from space through the full depth of the cloud. The strong backscattered radiation from the cloud aerosols indicates the presence of the cloud. A sharp drop off in the signal returns would signify the cloud bottom. Two problems exist with the conventional approach. The first problem is that thick clouds strongly attenuate light. Representative round-trip cloud extinctions are between 200 to 1000 dB per km. The second problem is multiple scattering from the cloud aerosols. This effect produces pulse stretching that prevents delineation of the sharp cloud bottom. These and other disadvantages are solved or reduced using the present invention.